sleep

Sleep is a naturally recurring altered state of consciousness with relatively suspended sensory and motor activity, characterized by the inactivity of nearly all voluntary muscles.[1] It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, but it is more easily reversible than hibernation or coma. Sleep is a heightened anabolic state, accentuating the growth and rejuvenation of the immune, nervous, skeletal and muscular systems. It is observed in all mammals, all birds, and many reptiles, amphibians, and fish.Physiology Sleep stagesIn mammals and birds, sleep is divided into two broad types: rapid eye movement (REM) and non-rapid eye movement (NREM or non-REM) sleep. Each type has a distinct set of associated physiological, neurological, and psychological features. The American Academy of Sleep Medicine (AASM) further divides NREM into three stages: N1, N2, and N3, the last of which is also called delta sleep or slow-wave sleep (SWS).Sleep proceeds in cycles of REM and NREM, the order normally being N1 → N2 → N3 → N2 → REM. There is a greater amount of deep sleep (stage N3) early in the night, while the proportion of REM sleep increases later in the night and just before natural awakening. Hours by ageChildren need more sleep per day in order to develop and function properly: up to 18 hours for newborn babies, with a declining rate as a child ages. A newborn baby spends almost 9 hours a day in REM sleep. By the age of five or so, only slightly over two hours is spent in REM.Age and condition Average amount of sleep per dayNewborn up to 18 hours1–12 months 14–18 hours1–3 years 12–15 hours3–5 years 11–13 hours5–12 years 9–11 hoursAdolescents9–10 hoursAdults, including elderly 7–8(+) hoursPregnant women 8(+) hoursSleep debtSleep debt is the effect of not getting enough rest and sleep; a large debt causes mental, emotional, and physical fatigue.

Sleep debt results in diminished abilities to perform high-level cognitive functions. Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure. GeneticsIt is suspected that a considerable amount of sleep-related behavior, such as when and how long a person needs to sleep, is regulated by our genetics. Hypnotics• Nonbenzodiazepine hypnotics such as eszopiclone (Lunesta), zaleplon (Sonata), and zolpidem (Ambien) are commonly used as sleep aids prescribed by doctors to treat forms of insomnia. Nonbenzodiazopines are the most commonly prescribed and OTC sleep aids used worldwide and have been greatly growing in use since the 1990s. They target the GABAA receptor.• Benzodiazepines target the GABAA receptor also, and as such, they are commonly used sleep aids as well, though benzodiazepines have been found to decrease REM sleep.• Antihistamines, such as diphenhydramine (Benadryl) and doxylamine (found in various OTC medicines, such as NyQuil)• Alcohol – Often, people start drinking alcohol in order to get to sleep (alcohol is initially a sedative and will cause somnolence, encouraging sleep) However, being addicted to alcohol can lead to disrupted sleep, because alcohol has a rebound effect later in the night. As a result, there is strong evidence linking alcoholism and forms of insomnia. Alcohol also reduces REM sleep.• Barbiturates cause drowsiness and have actions similar to alcohol in that it has a rebound effect and inhibits REM sleep, so it is not used as a long term sleep aid.• Melatonin is a naturally occurring hormone that regulates sleepiness. It is made in the brain, where tryptophan is converted into serotonin and then into melatonin, which is released at night by the pineal gland to induce and maintain sleep. Melatonin supplementation may be used as a sleep aid, both as a hypnotic and as a chronobiotic (see phase response curve, PRC).• Siesta and the "post-lunch dip" – Many people have a temporary drop in alertness in the early afternoon, commonly known as the "post-lunch dip." While a large meal can make a person feel sleepy, the post-lunch dip is mostly an effect of the biological clock. People naturally feel most sleepy (have the greatest "drive for sleep") at two times of the day about 12 hours apart—for example, at 2:00 a.m. and 2:00 p.m. At those two times, the body clock "kicks in." At about 2 p.m. (14:00), it overrides the homeostatic buildup of sleep debt, allowing several more hours of wakefulness. At about 2 a.m. (02:00), with the daily sleep debt paid off, it "kicks in" again to ensure a few more hours of sleep.• Tryptophan – The amino acid tryptophan is a building block of proteins. It has been claimed to contribute to sleepiness, since it is a precursor of the neurotransmitter serotonin, involved in sleep regulation. However, no solid data have ever linked modest dietary changes in tryptophan to changes in sleep. Stimulants• Amphetamines (amphetamine, dextroamphetamine, methamphetamine, etc.) are often used to treat narcolepsy and ADHD disorders and when used recreationally may be referred to as "speed." Their most common effects are anxiety, insomnia, stimulation, increased alertness, and decreased hunger.• Caffeine is a stimulant that works by slowing the action of the hormones in the brain that cause somnolence, particularly by acting as an antagonist at adenosine receptors. Effective dosage is individual, in part dependent on prior usage. It can cause a rapid reduction in alertness as it wears off.• Cocaine and crack cocaine – Studies on cocaine have shown its effects to be mediated through the circadian rhythm system. This may be related to the onset of hypersomnia (oversleeping) in regard to "Cocaine-Induced Sleep Disorder."[53]• Energy Drinks – The stimulating effects of energy drinks come from stimulants such as caffeine, and sugars, and they will eventually create a rapid reduction in alertness similar to that of caffeine.• MDMA, including similar drugs like MDA, MMDA, or bk-MDMA – The class of drugs called empathogen-entactogens keep users awake with intense euphoria. Commonly known as "ecstasy."• Methylphenidate – Commonly known by the brand names Ritalin and Concerta, methylphenidate is similar in action to amphetamines and cocaine.• Other Analeptic drugs like Modafinil and Armodafinil are prescribed to treat narcolepsy, hypersomnia, shift work sleep disorder, and other conditions causing Excessive Daytime Sleepiness. The precise mechanism of these CNS stimulants is not known, but they have been shown to increase both the release of monoamines and levels of hypothalamic histamine, thereby promoting wakefulness